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TI-2026-79436 Aliases CVE-2026-115349GHSA-4239-8pr8-4pwv

Quadratic parsing in Mistune lets crafted markdown exhaust CPU

Priority MEDIUM 44CWE-1333Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Partial Red Hat: 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-1333.

Summary

Mistune from 3.0.0 before 3.3.0 by lepture contains an algorithmic complexity flaw in the parse_link_text function in src/mistune/helpers.py. The flaw, cited as CWE-1333, makes parsing time quadratic when markdown contains deeply nested square brackets. A remote, unauthenticated attacker can send small crafted requests that exhaust server CPU.

Written with Claude Haiku 5.5 from the sources below · 2026-11-02

Description from the CNA

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00344 28th percentileScored 2026-11-07
Fix Partial mistune (lepture): 3.3.0Red Hat: 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
lepturemistune3.0.0 to before 3.3.03.3.0Patch availableCNA
  • mistune Vendorlepture Affected 3.0.0 to before 3.3.0 Fixed in 3.3.0 Patch available CNA

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*——lepture
  • cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:* Versions — — ·lepture

Remediation

Upgrade lepture Mistune to 3.3.0, the fixed version. Red Hat OpenShift AI (RHOAI) is affected, and Red Hat lists its plan as none available.

Written with Claude Haiku 5.5 from the sources below · 2026-11-02

  • Fix · CNA mistune (lepture) Fixed in 3.3.0

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    lepture mistune 3.3.0

    9 records Highest priority Priority HIGH 1 HIGH, 7 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2026-79440 Path traversal in Mistune include directive lets attackers read filesPriority HIGH 79
    • TI-2026-79441 Path traversal in Mistune lets attackers read local filesPriority MEDIUM 64
    • TI-2026-79438 CSS injection in Mistune figure directive figwidth optionPriority MEDIUM 57
    Show all 9 records →

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet
Not affected: 2 products
  • Red Hat OpenShift AI (RHOAI)
  • Red Hat OpenShift Container Platform 4

Timeline

  1. 2026-10-22 Threatist record created from CVE-2026-115349
  2. 2026-10-22 Alias added: GHSA-4239-8pr8-4pwv
  3. 2026-10-23 Affected versions changed · Red Hat
  4. 2026-10-23 CVSS score added · Red Hat
  5. 2026-10-23 Priority changed: MEDIUM → LOW
  6. 2026-10-26 CISA SSVC decision points changed
  7. 2026-10-26 Priority changed: LOW → MEDIUM
  8. 2026-11-02 Affected versions changed · Red Hat

References

Advisory 1

  • TI-2026-79440 Path traversal in Mistune include directive lets attackers read files CVSS 4.0CRITICAL 9.2
  • TI-2026-36755 Mistune: Potential DoS via quadratic-time parsing in parse_link_text CVSS 4.0HIGH 8.7
  • TI-2026-25521 Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles CVSS 4.0HIGH 8.7
  • TI-2026-53257 Mistune has Denial of Service — RecursionError via Excessive Emphasis Markers in Markdown CVSS 3.1HIGH 7.5
  • TI-2026-42736 Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions CVSS 3.1HIGH 7.5
  • TI-2026-42730 Regular expression denial of service in lepture mistune CVSS 3.1HIGH 7.5
See all 30 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences